Field of the Invention
This invention generally relates to a bicycle bottom bracket assembly. More specifically, the present invention relates to a bicycle bottom bracket assembly having a radially inward force reducing structure for reducing a radially inward force being transmitted to the bearing unit.
Background Information
Bicycling is becoming an increasingly more popular form of recreation, as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One area that has been extensively redesigned over the years is the bicycle bottom bracket, which is often called a bottom bracket.
Generally speaking, a conventional bicycle has a pair of wheels mounted to a diamond-shaped main frame formed of a plurality of tubes and a front fork pivotally connected to the main frame. The tubes of the main frame typically include a top tube, a down tube, a head tube, a seat tube, a pair of seat stays, a pair of chain stays and a cylindrical or tubular hanger part. The tubes of the main frame are fixedly coupled together to form a front triangularly shaped part and a rear triangularly shaped part that is arranged rearward of the front triangularly shaped part. The front and rear triangularly shaped parts serve as the framework of the bicycle body with a rear wheel mounted to the rear triangularly shaped part by a rear axle. The front fork is pivotally supported on the front triangularly shaped part such that the front fork can rotate freely about an axis that is tilted slightly from vertical. The front fork has a front wheel coupled thereto by a front axle.
The cylindrical or tubular hanger part of the frame is often called a bicycle bottom bracket hanger because it supports a bottom bracket assembly. Many different types of bottom bracket assemblies are currently available on the market. Generally speaking, a conventional bicycle bottom bracket assembly has a pair of bearing units mounted into a tubular hanger part of a bicycle frame for rotatably supporting a crank axle. One type of a conventional crank axle assembly is disclosed in U.S. Pat. No. 6,983,672. This conventional crank axle assembly is equipped with first and second support members that have first and second bearing units, respectively. The first and second support members are screwed into both end portions of the hanger part separately. The crank axle is rotatably supported on both of the first and second bearing units, and right and left cranks are non-rotatably mounted on the both axial end portions of the crank axle. Sometimes the first and second support members are press-fitted in to both end portions of the hanger part. One example of a conventional crank axle assembly that has the first and second support members press-fitted into the hanger part is disclosed in U.S. Pat. No. 7,503,700.
However, the first and second support members can be deformed radially inwardly due to a tightening force when the first and second support members are mounted in the hanger part of the bicycle frame. The deformation force tends to be larger when the first and second support members are made of a resin material. For example, when the first and second support members are screwed into the hanger part, the screwing force imparts a radially inward force that deforms the first and second support members radially inwardly. When the first and second support members are press-fitted into the hanger part, the press-fitting imparts a radially inward force that deforms the first and second support members radially inwardly. The radially inward deformation of the first and second support members negatively affects operation of the bearing units such that increased rotational torque is required to be exerted by the cyclist on the first and second cranks. Additionally, such deformation can damage the bearing units and shorten the service life thereof.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved bicycle bottom bracket assembly. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.